Configurable power distribution circuit

ABSTRACT

Briefly, in accordance with one embodiment of the invention, a circuit includes: a physical arrangement of power transistors. The circuit is adapted to couple a node to a power bus segment. The physical arrangement of power transistors is electronically configurable, based on externally derived electrical signals, to sink power to the node from the power bus segment, source power from the node to the power bus segment, and distribute power through the node

RELATED APPLICATION

[0001] This patent application is related to U.S. patent applicationSer. No. 08/954,334, titled “Circuit and Method for Power DistributionManagement,⇄ filed Oct. 17, 1997, by Steven R. Bard, assigned to theassignee of the present invention, and herein incorporated by reference.

BACKGROUND

[0002] 1. Field of the Invention

[0003] The present invention relates to a power distribution circuitand, more particularly, to a configurable power distribution circuit.

[0004] 2. Background Information

[0005] In a variety of situations, it is desirable to have the abilityto transfer power between different systems or devices. It might bedesirable, for example, to have the capability for a notebook computerto provide operating power to an attached peripheral device, such as acamera or a scanner. Likewise, it might be desirable for a personalcomputer (PC) docking station to provide operating power to a notebookcomputer docked to that PC docking station, such as via a power bus orpower distribution cable, for example.

[0006] This capability, however, introduces complexities related toconfiguring the power source/sink relationships between a set of devicesor systems. Of course, in this context, power source/sink relationshipsincludes relationships in which power is neither sourced nor sinked,such as in a “pass through” relationship, as explained in more detailherein. (Likewise, the terms “source/sink” and “sink/source” are usedinterchangeably.) It would be desirable if a circuit or technique wereavailable to address these power distribution complexities.

SUMMARY

[0007] Briefly, in accordance with one embodiment of the invention, acircuit includes: a physical arrangement of power transistors. Thecircuit is adapted to couple a node to a power bus segment. The physicalarrangement of power transistors is electronically configurable, basedon externally derived electrical signals, to sink power to the node fromthe bus segment, source power from the node to the bus segment, anddistribute power through the node.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The subject matter regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, however, both as to organization, andmethod of operation, together with objects, features, and advantagesthereof, may best be understood by reference to the following detaileddescription, when read with the accompanying drawings, in which:

[0009]FIG. 1 is a circuit diagram illustrating an embodiment of aconfigurable power distribution circuit in accordance with theinvention;

[0010]FIG. 2 is a block diagram illustrating an embodiment of a nodecomplying with the IEEE 1394 specification that may employ an embodimentof a configurable power distribution circuit in accordance with theinvention;

[0011]FIG. 3 is a schematic diagram illustrating an embodiment of anetwork employing an embodiment of a configurable power distributioncircuit in accordance with the invention;

[0012]FIG. 4 is a table of possible configurations for the embodiment ofFIG. 1;

[0013]FIG. 5 is a circuit diagram illustrating an embodiment of aconfigurable power distribution circuit in accordance with the inventioncoupled to a generalized node; and

[0014]FIG. 6 is a schematic diagram illustrating power source selectionand associated relationships for a node.

DETAILED DESCRIPTION

[0015] In the following detailed description, specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the relevant art thatthe present invention may be practiced without these specific details.In other instances, well-known methods, procedures, components, andcircuits have not been described in detail so as not to obscure thepresent invention.

[0016]FIG. 1 is a circuit diagram illustrating an embodiment 100 of aconfigurable power distribution circuit in accordance with the presentinvention. Of course, many embodiments are possible and the invention isnot limited in scope to the one illustrated. For example, although theinvention is not limited scope in this respect, embodiment 100 isillustrated as embodied on an integrated circuit (IC) chip. Asillustrated in FIG. 1, embodiment 100 comprises a physical arrangementof power transistors, such as 160, 150, 130, 170, 180, 120, 1 10 and130. The integrated circuit is adapted to couple a node to; a power busor power bus segment, such as a power distribution bus or cable, herecomprising power bus segments 90, 105, and 95. Bus segment 105 comprisesa “pass-through” segment and is internal to the node in this embodiment.In this context, a power bus or power distribution cable includes acollection of power bus segments that are coupled via interveningelectrical circuitry. Likewise, in the context, a power bus segmentrefers to an electrical connection or coupling for transferring powerbetween or via electrically isolated sink, source or pass-through nodes.As illustrated in FIG. 1, the node in this embodiment comprises at leasta physical layer 190 and a link layer 222, although the invention is notlimited in scope in this respect. In this context, the term node refersto a bus or bus segment interface plus one or more coupled devices. Aswill be explained in more detail hereinafter, the physical arrangementof-power transistors is electronically configurable, based on externallyderived electronic or electrical signals, to sink power to the node froma bus segment or segments, source power from the node to a bus segmentor segments, and distribute power through the node, such as across apower bus segment or segments, to another node or nodes. Furthermore, aswill be explained in more detail, the physical arrangement of powertransistors are also electronically configurable so that the power bussegments comprising the power bus may be electrically isolated to form“power domains”, as explained in more detail hereinafter.

[0017] The IEEE 1394 specification, “IEEE Standard for a HighPerformance Serial Bus”, IEEE Std 1394-1995, Aug. 30, 1996, availablefrom Institute of Electrical and Electronics Engineers, Inc. (IEEE), 345East 47^(th) Street, New York, N.Y. 10017, (hereinafter 1394specification), describes a high speed serial bus that includes thecapability for sourcing power from one “node” to another over a powerbus coupling the nodes. As previously indicated, this power sourcingcapability might be used, for example, to allow a notebook computer toprovide operating power to an attached peripheral device, such as acamera or a scanner, although the invention is not limited in scope tothis example. It might also enable a PC docking station to provideoperating power, via a 1394 specification compliant cable or bus, forexample, to a docked notebook computer. However, as previouslyindicated, this power sourcing capability introduces potentialcomplexities into the process of configuring the power source/sinkrelationships between a set of devices or systems, such as those coupledby a 1394 specification compliant bus. For example, at any given time,one device should be providing or sourcing power and the remainingdevices should either consume power as a power sink, power themselves,or act as a power “conduit” distributing power from the power source todevices coupled to the power distribution bus or cable (but not directlycoupled to the power source).

[0018] This situation is made more complex because a 1394 specificationcompliant device or system may operate in any one of several statesranging from full functionality to a powered-down state with limitedfunctionality. Depending on the particular situation, this may result ina 1394 specification compliant bus being effectively separated intodisjoint power bus segments (e.g., the bus may become “fragmented”). Inthis context, the term disjoint refers to power bus segments that areelectrically isolated from each other. This may result in problems forbus or cable powered devices or systems located downstream relative tothe bus or cable power source. In other words, the power provided by thepower source might not be transferred to the bus segment that isdisjoint from the bus segment directly coupled to the power source, thusrendering devices on such disjoint segments non-functional.

[0019] Using the 1394 specification as one example only, a 1394specification compliant interface has a tiered structure including threelayers: the PHY, link and transaction layers. In one embodiment, thephysical-interface layer, or PHY, may provide an electrical interface toa 1394 specification compliant cable. The PHY includes primarily analogcircuitry, including per-port functions, such as bus-port receivers,transmitters and signal-level comparators, and functions which may beshared across ports, such as bit-stream encoders, decoders,synchronization circuits and clock-generation circuits (phase-lockedloops). The link layer may provide packetizing services, and mayintervene between the PHY and the higher-level transaction layer. Thelink layer may comprise digital circuitry to perform data serializationand deserialization, data framing and checking, isochronous (e.g.,guaranteed-bandwidth) cycle control, and, perhaps, packet buffering, forexample. The transaction layer may comprise a digital hardware andsoftware structure which may provide three types of packet-basedtransactions: read, write and lock (to allow atomic, or indivisible,transaction sequences). For a 1394 specification compliant node, allhigher-level 1394 protocols make use of the transaction layer. Twolow-power operating modes are being proposed for inclusion in a new IEEEspecification or standard, being referred to informally as “the 1394 aspecification” and available in draft form, such as currently, draft0.9, from IEEE. A “standby” mode allows an interface to continue topropagate bus traffic, while a device attached to the bus through thatinterface is in a “sleep” state. The “suspend” state or mode savessubstantially more power, at the cost of not permitting the bus toprocess packet traffic. Rather, in the suspend state or made, nodescoupled to the bus are only able to generate or receive “wake-up”events, such as changes in node battery state, occurrence of a telephony“ring-indicate” signal, etc. In a normal operating state, a 1394specification compliant node's PHY and link layer are both power on.This is not the case in low-power states. In standby, for example, thePHY is powered, but only portions of the link layer are on or operating.In suspend, the link layer is off or not operating, and the PHY isreceiving low-current “trickle” power. In addition to varying thecurrent and voltage levels for a node's PHY and link layers, the lattermay draw power from either of two sources: either from a 1394specification compliant cable, or from a power source located within thenode. A link layer's or PHY's power source may change over time, such aswhen a battery-powered node switches to a just acquired alternatingcurrent (AC) power source. Therefore, having the capability to make thisselection would be a desirable feature. Of course, the 1394specification is provided only as an example and the invention is notrestricted in scope to use with buses or nodes that only comply with the1394 specification.

[0020]FIG. 2 is a schematic diagram illustrating an embodiment of a nodecoupled to a signal bus compliant with the 1394 specification. Ofcourse, again, the invention is not restricted in scope to use in thisparticular embodiment. Thus, again, the invention is not restricted inscope to use in connection with a 1394 specification compliant bus. Inthis particular embodiment, however, a 1394 specification compliant nodeincludes at least a physical layer (PHY) and a link layer, as previouslyindicated. A physical layer is directly coupled to a bus signal path,such as bus signal path 210 illustrated in FIG. 2. As illustrated inFIG. 2, physical layer 220 has one port. FIG. 2 illustrates analogtransceiver 230 coupled to bus signal path 210 via this port. In a 1394specification compliant bus, each port is coupled to one other port,resulting in a point-to-point structure; however, packets are routed toall active nodes providing the ability for a node to communicate withany other node. Physical layer 220 includes typically operations, suchas clock generation and signal encoding and decoding. Therefore, theanalog signals received via a signal path 210 are decoded into digitalsignals to be provided to link layer 240. Likewise, binary digitalsignals or bits provided in a bit stream via link layer 240 to physicallayer 220 are encoded by physical layer 220 for transmission via bussignal path 210. As indicated, the link layer performs packet processingtypically, such as bit serialization, bit deserialization, addressing,packet assembly, and packet disassembly. Likewise, transaction layer 260performs operations, such as reading, writing and atomic, orindivisible, read-modify-write cycles, as described. In this particularembodiment, 270 comprises an Open Host Controller Interface (OHCI)specification compliant device which is coupled to a host computersystem 280, such as a personal computer (PC), although the invention isnot limited in scope in this respect.

[0021] Physical layer 220, in FIG. 2, does not handle the node's powerrequirements in this embodiment; however, an embodiment of the inventionmight be used in an environment where it includes power switchingcircuits or input-output ports to support external power switchingsignals. In this embodiment, however, a power distribution network isseparate from, but operates in parallel with, the signal paths. In thiscontext, a power distribution network refers to the network coupling aself-contained or independent set of power source/sink relationshipsbetween a plurality of nodes coupled via a collection of power cable orpower bus segments, referred to here as a power cable or power bus. Thepower-distribution network may either accept power into the node or fromthe bus, it may feed power from the node onto the bus, it may pass ordistribute bus power through the node, enabling other nodes or it mayfragment the power network into independent “power domains” at the node.However, as previously described a 1394 specification compliant node maybe in any one of several operational or power states. The node's powerstate affects the operation of the device's physical layer, whichprovides an electrical interface for transferring data and control, andits link layer, which provides packet processing operations. A node'sPHY and link layer may have different and independent power requirementsin different power states. In addition, it may be desirable toreconfigure a node's power bus based at least in part on the node'sstate since the signal path capabilities of the node may be employed formanagement of the power bus. Without this, for example, the powernetwork of a 1394 specification compliant power,bus may effectively bedivided into two disjoint or electrically isolated bus segments, whichmay result in problems for bus or cable-powered devices or systemslocated downstream of the interrupting node relative to the presentpower source.

[0022] In another undesirable situation, a node coupling a power sourceto a power consumer or sink may be in a low power or “disabled” state.The power source will be unable to communicate with the power consumerthat is using or possibly even exhausting supplied power. Likewise,power utilization by the power consumer “behind” the disabled node (withrespect to the power source) may increase, resulting in a drain of evenmore power potentially. Thus, scenarios exist in which the powerutilized may become effectively unmanageable.

[0023] The embodiment illustrated in FIG. 1 comprises a mechanism ortechnique for performing configurable or reconfigurable powerdistribution, such as over a 1394 specification compliant bus, althoughthe invention is not limited in scope to buses complying with the 1394specification. This embodiment includes the capability to independentlyselect the power sources for a 1394 specification compliant node'sphysical and link layers, by drawing from an internal power source or apower source available via the power bus. Likewise, it includes theability for the 1394 compliant power bus to be partitioned at the node,resulting in two independently manageable, electrically isolated, powerbus segments or “power domains” on either side of the node. Therefore,each resultant “bus segment” may include its own set of distinct orparticular power source/sink relationships. Likewise, this particularembodiment includes the capability for a node to selectively supplypower to either or both of these two power bus segments or to the powerbus as a whole, forming a single power domain from adjacent andelectrically coupled power-bus segments.

[0024] In FIG. 1, physical layer 190 and link layer 222 are illustratedat the top of the figure along with an optional node internal powersource 212 which may be employed to supply power to the power bus or tothe node's PHY and/or link layer. Likewise, although the invention isnot limited in scope in this respect, the configurable powerdistribution circuit is illustrated as embodied on a separate integratedcircuit. Physical layer 190 may be configured to draw power either fromthe node's internal power source 212 or from the power bus, morespecifically from bus segment 90, but observe that segment 90 may alsobe electrically linked to power bus segments 105 and 95 through powertransistors, such as power field effect transistors (FETs) 110 and 120.Thus, PHY 190 may draw power from bus segments 90 or 95, for example.This may be accomplished in this embodiment by setting the controlsignal of a physical layer selector switch, such as D;.to a “one” or toa “zero” to select power from segment 90 or internal power,respectively, assuming, for example, that 160 and 180 compriseN-junction FETs and 130 and 150 comprise P-junction FETs. In thisembodiment, the physical layer selector switch is implemented as a pairof power transistors and voltage signals having a voltage signal levelindicating a logical “one” or “zero” are applied to the transistors'gates. Of course, power bipolar transistors might alternatively beemployed. Likewise, the control signal for transistors 130 and 180select the power source for the link layer/device in a similar manner.

[0025] As illustrated, two field effect transistors (FETs) 110 and 120are interspersed serially in the power bus. Control signals may beapplied to these FETs so that bus segments 90 and 95 of the power buscouple to or electrically isolate from one another. In addition, in thisembodiment, FET 170 is employed to enable or disable current flow fromthe node's internal power supply 212 to internal bus segment 105. Inthis particular embodiment, a sufficient voltage applied to the gate oftransistor 110 enables current flow across the associated FET and,likewise, for transistor 120, from the node's internal power supply tothe power bus. Likewise, in this embodiment; a diode 140 is included inthe current flow path. In this embodiment, this protective diode isemployed to ensure that power does not flow into the node's internalpower source in the event that a higher voltage power source is coupledto the power bus.

[0026]FIG. 4 is a table describing the operation of this particularembodiment. The left portion of the table provides the possiblecombinations of the five control signals that may be applied to thisparticular embodiment. The right portion of the table provides thephysical layer and link layer power source selections resulting from theassociated control signal states as well as the relationship of the bussegments. It should be noted that the table includes some redundancy inthat different applied control signals provide the same results Withrespect to power source selections. Therefore, the redundant rows may beeliminated without a loss of capability in this particular embodiment.This is illustrated in FIG. 4 by shading for the redundant rows. Forexample, table rows 5, 9, and 17 implement the same switching mechanismas that of row 1, and, thus, may be eliminated.

[0027] Based on the previous description, a situation might occur inwhich a first node=3 s internal power source is enabled to supply powerto the cable, and the first node's physical layer and link layer areconfigured to draw power from the-cable, yet the first node's physicaland link layers do not obtain power from the first node's internalsupply. For example, a higher voltage source of a second node may alsobe coupled to the power bus. The second node may actually supply the buspower including that drawn by the first node's physical layer and linklayer. In this situation, the first node's protective diode preventspower from flowing into the first node's internal supply.

[0028] Of course, the invention is not limited in scope to thisparticular embodiment or to an embodiment that includes all of theoperational functionality previously described. Depending upon thesituation, it may be desirable to employ a node with less than fullfunctionality. For example, again, using the 1394 specification as anexample, the physical layer and link layer may be designed orconstructed to only obtain power from the power bus, and, therefore, aninternal supply may not be needed. Likewise, depending upon thesituation, it may not be desirable to employ power transistors (e.g.,110 and 120 in FIG. 1) to provide separate power domains. The advantagesof these embodiments in which less than full functionality is employedincludes saving the cost of power transistors and associated controllogic. Likewise, it may not be desirable for every node to include thefunctionality previously described. It may depend, for example, on theparticular devices or systems coupled to the power bus. For example,some nodes may comprise “smart” devices or systems, while some maycomprise “dumb” devices or systems. For example, the power bus may beemployed to couple a camera to a PC. Typically, a camera may not beutilized as a cable power source, and therefore, the expense of aconfigurable power distribution circuit may not be justified.Alternatively, of course, a PC may typically include a variety ofoperational states and including an embodiment of a configurable powerdistribution circuit in accordance with the invention for a PC node maybe desirable.

[0029] This particular embodiment is adequate to provide support forsoftware control of all power configuration needs for a power buscomplying with the 1394 specification. This configuration capability isparticularly advantageous in mobile platform implementations of the 1394specification, so that a notebook computer may switch between internalbattery power, an alternating current (AC) power “brick”, or cablepower. Devices may couple to or decouple from the power bus at any timewhere this particular embodiment or alternative embodiments areemployed. Likewise, a mix of bus-powered and self-powered devices may becoupled to the power bus.

[0030]FIG. 3 is a block diagram illustrating an embodiment of two nodesof a network employing the embodiment of FIG. 1. This particularembodiment illustrates two nodes coupled to a power bus that is dividedor electrically isolated into three power bus segments. As illustratedin FIG. 3, node 310 includes physical layer 330 which is powered by nodeinternal power source 340. Likewise, link layer 350 for node 310 ispowered by internal power source 340. Internal power node source 340 isalso providing power to bus power segments 374 and 376. In contrast,physical layer 360 for node 370 is powered from power bus segment 376(and, therefore from node 310's internal power source under theprescribed switch settings). Link layer 380 of node 320 is powered fromsegment 377. Furthermore, the node internal power source of node 320 isinactive or not providing power and power bus segment 376 iselectrically isolated from segment 377. Segment 375 is configured to beelectrically isolated from the power bus.

[0031] Although the previous embodiments have been described inconnection with the 1394 specification, any cable power distributionsystem may make use of an embodiment of the invention. For example, anembodiment of the invention may be employed in connection with theUniversal Serial Bus (USB) specification, available from the UniversalSerial Bus-Implementers Forum, 2111 N.E. 25th Ave., MS JF2-51,Hillsboro, Oreg. 97124. Likewise, one embodiment of the invention may beemployed for use with a variety of different serial bus poweringsystems, including those compliant with different specifications, suchas USB or 1394. Furthermore, this power distribution scheme may also beused with parallel buses. As the previous embodiments and discussionillustrates, an embodiment of a configurable power distribution circuitin accordance with the invention provides a power distributioncapability and this capability is independent of the parallel or serialsignaling nature of the bus.

[0032]FIG. 5 is a circuit diagram illustrating an embodiment 500 of aconfigurable power distribution circuit in accordance with the inventioncoupled to a generalized node 510. The diagram also indicates the flowof power and the electrical coupling relationships, such as between bussegments 520, 530, and 540. FIG. 6 alternatively is a schematic diagramdepicting in a conceptual fashion the power source selection andassociated relationships for a particular node. As illustrated, aparticular node may select either an internal source for power orexternal source for power, depicted by power source selection 610.Likewise, either of these power sources may be obtained via a powersource selection made between a variety of bus segments for theselection of an external source, as for 620, or made between a varietyof internal power sources for the selection of an internal source, asfor 630.

[0033] An embodiment of a configurable power distribution circuit inaccordance with the invention, such as previously described, may beemployed to implement an embodiment of a method for distributing powerin accordance with the invention as follows. In this embodiment, poweris distributed among a plurality of nodes. Portions of the power bus maybe electrically isolated into power bus segments, such as at least twosegments, such as by using an embodiment previously described, forexample. Of course, more than two power bus segments may also beemployed. Then, particular sets of power sink/source relationships amongthe nodes may be configured. In this embodiment, the particular nodesmay be coupled to the respective power bus segments previouslydescribed, for example. Although the invention is not limited in scopeto being employed in connection with the 1394 specification or a 1394specification compliant bus or node, where a 1394 specificationcompliant bus or node is employed, each node comprises at least aphysical layer and a link layer, as previously described. Furthermore,as previously described and illustrated, in embodiments of aconfigurable power distribution circuit in accordance with the presentinvention, the particular sets of power sink/source relationships amongthe nodes includes relationships that vary over time or are “timevarying”. In this particular embodiment, a particular set of powersink/source relationships among the nodes are configured by applyingexternally derived electrical signals to an electrically configurablephysical arrangement of power transistors, such as-previously described.The externally derived electrical signals may, for example, be providedby a personal computer operating in accordance with software loaded onthe computer that provides the desired electrical signals to configurethe physical arrangement of power transistors as desired. Of course, theinvention is not limited in scope in this respect.

[0034] In another embodiment of a method of distributing power inaccordance with the present invention, a plurality of nodes coupled viaa plurality of power bus segments may be configured to provide at leastone particular set of power sink/source relationships among the couplednodes. Therefore, in this embodiment, there may be one particular set ofpower sink/source relationships. Likewise, there may also be anotherparticular set of power sink/source relationships other than this oneparticular set of power sink/source relationships. For example, the twosets of particular source/sink relationships may be electricallyisolated and formed power bus segments, such as previously described.

[0035] While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes andequivalents will now occur to those skilled in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A circuit comprising: a physical arrangement of power transistors;said circuit being adapted to couple a node to a power bus segment; saidphysical arrangement of power transistors being electronicallyconfigurable, based on externally derived electrical signals, to sinkpower to the node from the power bus segment, source power from the nodeto the power bus segment, and distribute power through the node.
 2. Thecircuit of claim 1, wherein said arrangement of transistors are alsoelectronically configurable so that at least two power bus segments arecapable of being coupled to the node and electronically isolated fromeach other at the node.
 3. The circuit of claim 2, wherein saidtransistors comprise power field effect transistors (FETs).
 4. Thecircuit of claim 2, wherein said circuit is coupled to a bus fortransferring signals compliant with the 1394 specification.
 5. Thecircuit of claim 1, wherein the power bus segment comprises a power bussegment via which nodes with a particular set of power sink/sourcerelationships may be coupled.
 6. The circuit of claim 5, wherein saidparticular set of power sink/source relationships is time-varying. 7.The circuit of claim 1, wherein said node comprises at least a physicallayer and a link layer.
 8. The circuit of claim 1, wherein said physicalarrangement of power transistors is embodied on an integrated circuit(IC) chip.
 9. A method for distributing power among a plurality of nodesvia a power bus, comprising: electronically isolating portions of thepower bus into at least two power bus segments; and configuringparticular sets of power sink/source relationships among the nodescoupled to the respective power bus segments of said at least two powerbus segments.
 10. The method of claim 9, wherein said nodes eachcomprise at least a physical layer and a link layer.
 11. The method ofclaim 9, wherein configuring particular sets of power sink/sourcerelationships among the nodes comprises configuring time-varying powersink/source relationships among the nodes.
 12. The method of claim 9,wherein the nodes are also coupled by a bus comprising a bus fortransferring signals compliant with the 1394 specification.
 13. Themethod of claim 9, wherein configuring particular sets of powersink/source relationships among the nodes comprises applying externallyderived electrical signals to an electrically configurable physicalarrangement of power transistors.
 14. A method for distributing poweramong a plurality of nodes via a power bus coupling the plurality ofnodes together, comprising: configuring at least one particular set ofpower sink/source relationships among the nodes coupled via the powerbus.
 15. The method of claim 14, wherein configuring at least oneparticular set of power sink/source relationships comprises configuringanother particular set of power source/sink relationships other than theat least one particular set of power source/sink relationships.
 16. Themethod of claims 15, wherein the two sets of particular powersource/sink relationships are electrically isolated and form two powerbus segments.